A-M baby

Task/Forward-difference/C/forward-difference-1.c

@@ -0,0 +1,39 @@
+#include <stdlib.h>
+#include <string.h>
+#include <stdio.h>
+
+double* fwd_diff(double* x, unsigned int len, unsigned int order)
+{
+	unsigned int i, j;
+	double* y;
+
+	/* handle two special cases */
+	if (order >= len) return 0;
+
+	y = malloc(sizeof(double) * len);
+	if (!order) {
+		memcpy(y, x, sizeof(double) * len);
+		return y;
+	}
+
+	/* first order diff goes from x->y, later ones go from y->y */
+	for (j = 0; j < order; j++, x = y)
+		for (i = 0, len--; i < len; i++)
+			y[i] = x[i + 1] - x[i];
+
+	y = realloc(y, sizeof(double) * len);
+	return y;
+}
+
+int main(void)
+{
+	double *y, x[] = {90, 47, 58, 29, 22, 32, 55, 5, 55, 73};
+	int i, len = sizeof(x) / sizeof(x[0]);
+
+	y = fwd_diff(x, len, 1);
+	for (i = 0; i < len - 1; i++)
+		printf("%g ", y[i]);
+	putchar('\n');
+
+	return 0;
+}

Task/Forward-difference/C/forward-difference-2.c

@@ -0,0 +1,33 @@
+#include <stdio.h>
+
+int* binomCoeff(int n) {
+     int *b = calloc(n+1,sizeof(int));
+     int j;
+     b[0] = n%2 ? -1 : 1;
+     for (j=1 ; j<=n; j++)
+           b[j] = -b[j-1]*(n+1-j)/j;
+
+     return(b);
+};
+
+main () {
+    double array[] = { 90, 47, 58, 29, 22, 32, 55, 5, 55, 73 };
+    size_t lenArray = sizeof(array)/sizeof(array[0]);	
+
+    int p = 4;  // order
+    int *b = binomCoeff(p);   // pre-compute binomial coefficients for order p
+
+    int j, k;
+
+    // compute p-th difference
+    for (k=0 ; k < lenArray; k++)
+        for (array[k] *= b[0], j=1 ; j<=p; j++)
+            array[k] += b[j] * array[k+j];
+
+    free(b);
+
+    // resulting series is shorter by p elements
+    lenArray -= p; 	
+    for (k=0 ; k < lenArray; k++)  printf("%f ",array[k]);
+    printf("\n");
+}